Few cars seem to have them. My current audi has, our Fiat has not.

In any case the current Römer Kid Plus just uses the belt.

Our previous Izi BeSafe was non-isofix, but it actually beat all isofix systems that year. To install it you have to push the seat down into the carseat with your weight (no problem for me), then pull the belt tight. Then you close the two ‘ears’ of the seat and the tention will keep the seat quite stable. Then you pull out a tab below the seat which tightens the belt even more.

Our first (and second replacement after the crash) was a Dremefa EasyBob (now out of production as the brand got bought by Bébécar) also had to be pushed into the car seat and then the belt had to be clamped by a plastic thing fixing the seat into the car. It proved quite effective.

I’ve been reading the instruction on URLs you’ve mentioned. What I find weird is that there is no mentioning of the ALR (Automatic Locking Retractor) / KISI (Don’t know how it’s spelled, but I think it’s short for kindersicherheit or something) mechanism that’s some of the retractors have specially for child seats.

This mechanism is usually activated when you pull out all webbing. When you feed back webbing you will hear a clicking sound, and you can’t pull out any webbing anymore. This can be used to make the webbing tight and stay tight. The mechanism will unlock when you feed enough webbing back.

You also might want to read:
http://www.cpsafety.com/articles/lockincss.aspx
http://www.carsafety4kids.com/lockingclip.html

Kurt

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Without a third point the seat would rotate in a crash.

The main aim of this is to fix the child seat directly to the car, so we don’t depend on the seat (designed for an adult) to absorb the crash.

All the webbing I’ve seen stretches a lot. I think at 2500N it was in the order of 5 cm. But we don’t do any tests on the webbing itself. I’ve seen them, but never really took a close look at them.

On the other hand we did test on the buckle by putting up to 10kN on it, at which points it’s deformed but should still open. I wouldn’t want to use that one again.

Then you can also have up to 3 pretensioners for a 3 point seatbelt, as most cars have. Those can fire at different points. Those should pull you back in your seat. And I wouldn’t want to that with webbing that didn’t stretch.